Tocotrienol inhibits secretion of angiogenic factors from human colorectal adenocarcinoma cells by suppressing hypoxia-inducible factor-1alpha.
Tocotrienol (T3), unsaturated vitamin E, has recently gained considerable attention as a potent antiangiogenic agent minimizing tumor growth, the exact intracellular mechanisms of which remain poorly understood. Because hypoxia-inducible factor-1alpha (HIF-1alpha), its downstream target vascular endothelial growth factor (VEGF), and other angiogenic factors such as interleukin-8 (IL-8) and cyclooxygenase 2 (COX-2) play critical roles in neovascularization, we tested the hypothesis that the inhibitory effect of T3 on tumor angiogenesis is via regulation of these angiogenic factors. We used 2 cancer cell lines, human colorectal adenocarcinoma cells (DLD-1) and human hepatoma cells (HepG2). T3 isomers (2 micromol/L) inhibited hypoxia-induced VEGF secretion from DLD-1, with delta-T3 showing potent inhibition. Delta-T3 suppressed hypoxia-induced VEGF and IL-8 expression in DLD-1 at both mRNA and protein levels, and we found the inhibitory mechanism of delta-T3 by reducing HIF-1alpha protein expression or increasing HIF-1alpha degradation. Also, delta-T3 (2 micromol/L) did not affect hypoxia-induced COX-2 mRNA expression; however, delta-T3 tended to suppress (P = 0.044) hypoxia-induced COX-2 protein expression, implying a possible post-transcriptional mechanism by delta-T3. Overall, our results confirmed that T3 has an inhibitory effect on angiogenic factor secretion from cancer cells and revealed the possible mechanisms, providing new information about the antiangiogenic effects of T3.
Shibata
Akira
A
Food and Biodynamic Chemistry Laboratory, Graduate School of Agricultural Science, Tohoku University, Sendai 981-8555, Japan.
Nakagawa
Kiyotaka
K
Sookwong
Phumon
P
Tsuduki
Tsuyoshi
T
Tomita
Shuhei
S
Shirakawa
Hitoshi
H
Komai
Michio
M
Miyazawa
Teruo
T
D042501:Angiogenic Proteins / Q000235:genetics / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D024508:Tocotrienols / Q000494:pharmacology*; D014157:Transcription Factors / Q000378:metabolism
D042501:Angiogenic Proteins; D000970:Antineoplastic Agents; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D012333:RNA, Messenger; D024508:Tocotrienols; D014157:Transcription Factors